Include wctype.h in wchar.h as an XSI extension

However, note that this inclusion is obsolescent in SUSv4 and therefore
may be removed in the next revision.

http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/wchar.h.html

Signed-off-by: Yaakov Selkowitz <yselkowi@redhat.com>

newlib/libc/include/wchar.h

@@ -20,6 +20,10 @@
 /* For __STDC_ISO_10646__ */
 #include <sys/features.h>
 
+#if __XSI_VISIBLE /* && __XSI_VISIBLE < 800 */
+#include <wctype.h>
+#endif
+
 #ifndef WEOF
 # define WEOF ((wint_t)-1)
 #endif